U.S. patent number 4,313,081 [Application Number 06/136,264] was granted by the patent office on 1982-01-26 for line drop compensation device for an electrical distribution system.
This patent grant is currently assigned to Caci, Inc. - Federal. Invention is credited to David W. Smith.
United States Patent |
4,313,081 |
Smith |
January 26, 1982 |
Line drop compensation device for an electrical distribution
system
Abstract
A line drop compensator device for an aircraft flight line
electrical distribution system has a plurality of service points
connected at spaced locations along a three-phase power line and
the current flow at each service point is sensed. In response to
the sensed current flow, capacitance is added between the conductor
lines and neutral of the power line so as to correct the voltage in
proportion to the demand. Compensation is thus added proportional
to the current drawn from the line.
Inventors: |
Smith; David W. (Alexandria,
VA) |
Assignee: |
Caci, Inc. - Federal
(Arlington, VA)
|
Family
ID: |
22472080 |
Appl.
No.: |
06/136,264 |
Filed: |
April 1, 1980 |
Current U.S.
Class: |
323/209;
307/31 |
Current CPC
Class: |
H02J
3/16 (20130101); Y02E 40/30 (20130101) |
Current International
Class: |
H02J
3/12 (20060101); H02J 3/16 (20060101); G05F
001/70 () |
Field of
Search: |
;307/11,31,33
;323/121,128,102,105,205,208,209,210 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shoop; William M.
Attorney, Agent or Firm: Jaskiewicz; Edmund M.
Claims
What is claimed is:
1. A line drop compensator device for a service point of an
aircraft flight line electrical distribution system comprising a
plurality of service points for aircraft connected at spaced
locations to a three-phase power line including a neutral line,
said power line connected to a single power source, means at each
of said service points for sensing the current flow at that service
point and generating a proportional signal, means at that service
point for comparing said proportional signal with a reference
signal and generating a control signal, and means at that service
point responsive to said control signal for adding capacitance
between a line and neutral to compensate for line inductance and
any lagging power factor caused by the aircraft load at that
service point so as to correct the voltage supplied to the aircraft
proportional to the demand.
2. A line drop compensator device as claimed in claim 1 and further
comprising means for connecting additional capacitance across the
phase conductor and neutral in response to predetermined increases
in the sensed current flow.
3. A line drop compensator device as claimed in claim 1 wherein
said current flow sensing means is in one phase conductor in the
power line.
4. A line drop compensator device as claimed in claim 3 wherein
said capacitance adding means comprises a control circuit connected
to said comparing means to receive said control signal and a
compensation circuit including a capacitance.
5. A line drop compensator device as claimed in claim 4 wherein
said control circuit and said compensation circuit are connected
across the neutral line and the phase conductors of said power
line.
6. A line drop compensator device as claimed in claim 4 and further
comprising a plurality of said control circuits and said
compensation circuits connectable across said neutral line and the
phase conductors of said power line.
7. A line drop compensator device as claimed in claim 6 and means
for connecting additional control circuits and capacitance circuits
across said neutral line and phase conductors of said power line at
predetermined increments of current flow sensed by said sensing
means.
Description
The present invention relates to an aircraft flight line electrical
distribution system, more particularly, to a dynamic line drop
compensator for such a system.
The servicing and starting of aircraft, particular jet aircraft, on
a flight line requires the ready availability of electrical energy
at a voltage within a close tolerance voltage range. The electrical
energy is provided through connector cables which extend along the
flight line and is connected to a suitable source of electrical
energy of a desired voltage and frequency. A plurality of spaced
service islands are connected along the connector cables and each
island has an aircraft service cable and a connector plug assembly.
The service islands and the connector cables may be positioned upon
the ground and covered with aluminum casting covers in order to
allow aircraft to taxi over the system.
Present day aircraft flight line electrical distribution systems
are capable of supporting aircraft requiring 6 KVA or less of
electrical energy for servicing. As new aircraft become available
which require larger amounts of electrical energy, the conductors
of the flight line may cause voltage losses which are sufficiently
large to reduce the voltage at each aircraft below that which the
aircraft can tolerate. Also, older aircraft are equipped with new
or updated electronic systems which require more energy for
servicing, thus causing voltage losses in the conductors to
increase which in turn reduces the voltage at each aircraft below
that level which the aircraft can tolerate.
It has been proposed to utilize a line drop compensator so as to
correct the voltage at the aircraft when multiple aircraft are
connected to a single power source. Such known line drop
compensators compensate for reactive losses in each load line. In
those instances where multiple loads are connected to a single
power source, attempting to correct the line drop by sensing total
load current will bring about severe under and over voltage
conditions in one or more of the multiple-load lines. Further, such
known line drop compensators will not correct the voltages at the
aircraft to 115.+-.2 volts in a flight line electrical distribution
system. The present known line drop compensators add capacity in
series with the line.
It is therefore the principal object of the present invention to
provide an improved aircraft flight line electrical distribution
system which makes available electrical energy at a voltage with a
close tolerance voltage range.
It is another object of the present invention to provide an
aircraft flight line electrical distribution system which corrects
the voltage at the aircraft when multiple aircraft are connected to
a single power source proportional to the demand.
It is an additional object of the present invention to provide such
an aircraft flight line electrical distribution system which senses
the number and location of the aircraft on the distribution network
and corrects the voltage proportional to the demand.
It is a further object of the present invention to provide a line
drop compensator for an aircraft flight line electrical
distribution system which can be packaged into a service island of
the system and which corrects the voltage at the aircraft when
multiple aircraft are connected to a single power source by sensing
the number and location of the aircraft and correcting the voltage
proportional to the demand.
The objects of the present invention are achieved and the
disadvantages of the prior art are eliminated by the aircraft
flight line electrical distribution system having a line drop
compensator according to the present invention. According to one
aspect of the present invention a line drop compensator device for
an aircraft flight line electrical distribution system may comprise
a plurality of service points for aircraft connected at spaced
locations to a three-phase power line including a neutral line. At
each service point there is means for sensing the current flow at
that service point and for generating a proportional signal. The
proportional signal is compared with a reference voltage and a
control signal is then generated. In response to the control signal
capacitance is added between the phase conductors of the power line
and neutral to compensate for line inductance and for any lagging
power factor caused by the aircraft load.
A plurality of compensating and control circuits may be provided so
as to add additional capacitance to predetermined increases in
current flow sensed in the power line at the service point.
Other objects and advantages of the present invention will be
apparent upon reference to the accompanying description when taken
in conjunction with the following drawings, which are exemplary,
wherein;
FIG. 1 is a top plan view of a portion of an aircraft flight line
electrical distribution system according to the present invention
showing several service points and aircraft at the service
points;
FIG. 2 is a perspective view of a service point in which is
incorporated the dynamic line drop compensator of the present
invention;
FIG. 3 is a schematic block diagram showing the electronic circuit
of the dynamic line drop compensator of the present invention;
and
FIG. 4 is a schematic diagram showing the electronic circuitry and
components of the block diagram of FIG. 3.
Proceeding next to the drawings wherein like reference symbols
indicate the same parts throughout the various views a specific
embodiment and modifications of the present invention will be
described in detail.
As may be seen in FIGS. 1 and 2, the aircraft flight line
electrical distribution system comprises a plurality of
interconnector cables 10 which extend along the flight line and are
connected to a suitable source of electrical energy to provide
115/200 VAC, three-phase 400 Hz electrical energy. Spaced along the
interconnector cables is a plurality of service points or islands
11 each of which is provided with an aircraft service cable 12, at
the end of which is an aircraft connector plug 13. There is also a
dynamic line drop compensator with each island and indicated at
14.
The interconnector cables may be connected to the service points by
detachable electrical connectors as known in the art. In a similar
manner the cables of the service cable 12 are connected to the
service points by connectors. All the electrical connections are
made to corresponding coupler components on the exterior of the
service island. The connectors are preferably of the water-proof,
quick-connector type.
The service islands 11 and interconnector cables 10 may be covered
by aluminum casting covers 15 and 16 to allow aircraft to taxi over
the system. The aluminum covers may be of the same type as
disclosed in U.S. Pat. No. 4 101 100 issued July 18, 1978. The
aluminum covers and the enclosure for the interconnector cables and
service points have such a height and shape to enable aircraft
tires to pass readily over these components and the enclosures and
covers are provided with suitable tie-down or fastener means so as
to be secured upon the flight line surface.
The dynamic line drop compensator which is schematically
illustrated in FIG. 3 adds capacitance from a line conductor to
neutral at various current levels drawn by the aircraft. The
interconnector cables 10 include a three-phase power line having
phase conductors A, B, and C and neutral line N, as shown in FIG.
3. A current sensor 17 which may be a current transformer or a Hall
generator is connected in phase conductor C and provides a
low-lever A.C. voltage signal at 18 proportional to the current
flow at the service island. This proportional signal is rectified
and compared to a D.C. voltage signal in a signal comparator
19.
A current signal is generated at 20 by the comparator 19 and
supplied to a control circuit 21 when the current level through the
sensor 17 reaches a level of approximately 17.3 amperes. The signal
20 received by the control circuit 21 closes relay contacts which
in turn connect a compensation circuit 22 to add capacitance
between phase conductor A and neutral N, phase conductor B and
neutral N and phase conductor C and neutral N. This capacitance is
selected to counteract the line inductance and any lagging power
factor which might be caused by the type of aircraft load.
The rectified signal received by the comparator circuit 19 may
continue to increase as the current through the sensor 17 increases
beyond 17.3 amperes to 34.6 amperes at which level the comparator
circuit 19 sends a control signal at 23 to control circuit 24
causing relay contactors to close. Thus, another set of capacitance
is added across phase conductors A, B, and C to neutral.
As the current through the current sensor 17 increases to 51.9
amperes another compensation 29 is added as a result of a control
signal from control circuit 25. This process of adding additional
capacitance continues in two more steps of 69.2 amperes and 86.5
amperes at which stage control circuits 26 and 27 are also actuated
generate control signals to compensation circuits 30 and 31 to
supply additional capacitance.
A power supply 32 conditions the 115 A.C. from phase A to supply
electrical energy to the electronic current sensor 17 and to supply
the comparators circuit 19 with the correct D.C. voltage.
The current levels at which the compensation circuits 22, 28, 29,
30, and 31 are added across phase conductors A, B, and C to neutral
can be varied as may be desired to selected magnitudes in the
current sensor circuit 17.
FIG. 4 shows in detail the circuitry and components of the block
diagram of FIG. 3. In order to initiate the power supply 32, it is
first necessary to insert the connector plug 13 into the aircraft
service recepticle as shown with the aircraft in FIG. 1. This will
then provide a current load from the phase C conductor to neutral
when the aircraft internal electrical system is activated. The
phase conductor C will then have a current flow and the current
sensor C.T. will generate an A.C. voltage signal proportional to
and at the same frequency as the current flowing through phase
conductor C. The amplitude of this signal will be 0.1 volt for each
ampere of current flowing through the current sensor C.T. When this
signal reaches a magnitude of about 1 volt, the power supply 32
will be turned on and will then supply the other circuits with the
condition 18 volt direct current. The voltage signal from the
current sensor CT will be then impressed upon the amplifier U.sub.1
through resistance R.sub.1. Resistances R.sub.1, R.sub.2 and
R.sub.3 are provided to establish the gain level of the amplifier
U.sub.1.
The output of amplifier U.sub.1 is rectified through diode D.sub.1
and filtered through capacitor C.sub.1 and resistor R.sub.4 to
produce a D.C. level. The D.C. voltage level is adjusted by
resistor R.sub.4 to a voltage level of 200 millivolts at the input
to the buffer amplifier U.sub.1 when 17.3 ampere current is flowing
through the current sensor CT.
The comparators U.sub.2, U.sub.3, U.sub.4, U.sub.5 and U.sub.6
compare the D.C. voltage level from the buffer amplifier U.sub.1 to
the present reference levels as provided by the voltage regulator
VR.sub.1 and the group of series resistors R.sub.5, R.sub.6,
R.sub.7, R.sub.8 and R.sub.9. The reference level at comparator
U.sub.2 is 1000 millivolts, at U.sub.3 is 800 millivolts, at
U.sub.4 is 600 millivolts, at U.sub.5 is 400 millivolts and at
U.sub.6 is 200 millivolts. When the D.C. voltage level from the
buffer amplifier U.sub.1 becomes greater than the reference voltage
(200 millivolts) across resistor R.sub.9, the output of the
comparator U.sub.6 will assume a high state causing transistor
Q.sub.5 to be forward biased into conduction. Transistor Q.sub.5
forms a series path to complete the conduction path for the relay
coils K.sub.13, K.sub.14 and K.sub.15 to maintain the contacts in
the energized state. Closing of the relay contacts S.sub.13,
S.sub.14 and S.sub.15 will connect the compensating capacitors
across the phase conductors A, B, and C to neutral N.
As the D.C. voltage level from the buffer amplifier U.sub.1
continues to be greater than the reference voltage of 400
millivolts across resistors R.sub.9 and R.sub.8, the output of the
comparator U.sub.5 will assume a high state causing transistor
Q.sub.4 to be forward biased into conduction. Transistor Q.sub.4
will thus form a series path to complete the conduction path for
the relay coils K.sub.10, K.sub.11 and K.sub.12 to maintain the
contact in the energized state. Closing of the relay contacts
S.sub.10, S.sub.11 and S.sub.12 will connect additional
compensating capacitors across the phase conductors A, B, and C to
neutral N.
As the D.C. voltage level from amplifier U.sub.1 continues to
increase with respect to the current flow through the current
sensor CT, additional comparators will change state and, thus, add
more compensating capacitance across the phase conductors A, B, and
C to neutral N in accordance with the following table.
TABLE 1
__________________________________________________________________________
Nominal Current Through Output State of Transistors Conducting
Current Sensor CT Q5 Q4 Q3 Q2 Q1
__________________________________________________________________________
below 17.3 ampere Not Not Not Not Not 17.3 ampere Conductiong Not
Not Not Not 34.6 ampere Conducting Conducting Not Not Not 51.9
ampere Conducting Conducting Conducting Not Not 69.2 ampere
Conducting Conducting Conducting Conducting Not Over 86.5 ampere
Conducting Conducting Conducting Conducting Conducting
__________________________________________________________________________
When the capacitors are added between the phase conductors A, B,
and C and neutral, the voltage at the aircraft will be increased by
a proportional amount such that the conductor inductive reactance
is canceled out by the capacitance.
While only five stages or levels of compensating capacitance are
illustrated in FIG. 4 it is to be understood that further levels of
capacitance may be added to the circuit as shown in FIG. 4. These
additional levels of capacitance may be as many as five or even
more.
An advantage of the present invention is that the voltages at the
aircraft can be maintained with a 115.+-.2 volts at the maximum
current carrying capacity of the interconnector cables. By
selectively adjusting the dynamic line drop compensator, the
voltage at the aircraft can be corrected to 115.+-.1.15 volts.
The dynamic line drop compensator is quite compact and can be
readily packaged into a cast box about 24 inches wide.times.10
inches deep.times.3 inches high.
The component values for the embodiment as disclosed in FIG. 4 are
shown in Table 2.
TABLE 2 ______________________________________ Capacitors C1 150
ufd. C2-C16 25 ufd. Resistors R1 2.7 k R2 1.0m R3 560 R4 1.0m
variable R5-R9 100 ______________________________________
It should also be borne in mind that the present invention can
utilize an integrated circuit that includes U.sub.1 through
U.sub.6, R.sub.5 through R.sub.9, Q.sub.1 through Q.sub.5 and
VR.sub.1. The relays K.sub.1, S.sub.1, K.sub.2, S.sub.2, etc. each
could then be a solid state relay.
It should further be borne in mind that the present invention can
be modified to incorporate a power factor transducer circuit that
will sense the variation in the power factor caused by the aircraft
load and adjust the voltage level at which the comparator assumes a
high state.
This modification would enable the dynamic line drop compensator to
adjust the voltage at the aircraft for either a change in current
or a change in the loads' power factor.
The block diagram of FIG. 3 essentially comprises a sense circuit,
a comparator circuit, compensator control circuit, voltage
compensation and the necessary power supply circuits.
The sense circuit consist of a current sensor and the necessary
amplifiers and filters to supply a voltage proportional to the
current in the aircraft cable. This voltage is then fed to a
comparator circuit which is an analogue level detector which
consists of independent comparators, a buffer, voltage regulator,
scaling resistor network and output drive resistor.
The open collector output transistors are controlled by independent
comparators. These open-collector output transistors are capable of
sinking up to 40 milliamperes when turned on and withstanding 18 to
34 volts in their off state. The output is switched to a low-logic
level at a typical input voltage of 200 millivolts. After each 200
millivolt step, the subsequent outputs are switched to a low-logic
level. This logic circuit will produce a logic change in the output
transistor as the current in the aircraft cable changes. The logic
switch points can be set as indicated above in Table 1.
Thus it can be seen that the dynamic line drop compensator at each
service point or island corrects the voltage at individual aircraft
when multiple aircraft are connected to a single power source. The
dynamic line drop compensator can be utilized in other electrical
distribution systems either supplying single or multi electrical
equipments. While the embodiment of the invention as disclosed
herein is used with a circuit of 400 Hz, it is to be borne in mind
that the line drop compensator device of the present invention may
be used at other electrical power line frequencies.
It will be understood that this invention is susceptible to
modification in order to adapt it to different usages and
conditions and, accordingly, it is desired to comprehend such
modifications within this invention as may fall within the scope of
the appended claims.
* * * * *